The present invention relates to the modulation of electromagnetic radiation and, more particularly, to a mechanical valve, and an array of such valves, for regulating the flow of radiation by selectively blocking the radiation.
Transmissive devices for modulating the flow of electromagnetic radiation, such as visible, infrared and ultraviolet radiation, are known. The simplest such devices are mechanical shutters. These devices have the advantage of being broad band, inasmuch as the materials used are opaque, in the thicknesses typically used, over a very wide spectral range; but typically these devices are too large to allow spatial modulation of the radiation on a short length scale approaching the wavelength of the radiation. In addition, their mechanical inertia places a lower bound on the time scale of this modulation. Spatial modulation on a short length scale, and temporal modulation on a short time scale, typically require the manipulation, by electrical, magnetic or electronic means, of the optical properties of substances such as liquid crystals. These optical properties generally are strong functions of wavelength, and so restrict the operation of such devices to particular spectral bands.
Reflective devices for fine spatial and temporal modulation of electromagnetic radiation over a relatively wide spectral range are known. These devices include, for example, the deformable mirror device described in U.S. Pat. No. 5,083,857 to Hornbeck. These devices typically consist of arrays of reflectors, each reflector corresponding to one pixel of a display. Such devices are inherently reflective, rather than transmissive, because the control electronics that addresses and activates each individual pixel is located behind the pixel, and would block the transmission of electromagnetic radiation across the pixel. Systems including such devices are inherently less compact than systems based on transmissive devices, because the light to be modulated must be directed at the device at an angle different from that at which the modulated, reflected light leaves the device.
There is thus a widely recognized need for, and it would be highly advantageous to have, a transmissive device, for fine spatial and temporal modulation of electromagnetic radiation, that operates over a wide spectral range.